Epitaxial oxide films via nitride conversion

ABSTRACT

The present invention relates to oxides on suitable substrates, as converted from nitride precursors.

The present invention is a divisional application of and claims prioritybenefit from application Ser. No. 09/931,588 filed on Aug. 16, 2001,issued as U.S. Pat. No. 6,645,639 on Nov. 11, 2003, which is herebyincorporated by reference and which is in turn a continuation-in-part ofapplication Ser. No. 09/687,940 filed on Oct. 13, 2000, now issued U.S.Pat. No. 6,573,209, which claims priority benefit therefrom.

CROSS-REFERENCE TO RELATED APPLICATIONS

The following relate to the present invention and are herebyincorporated by reference in their entirety: U.S. Pat. No. 5,739,086Structures Having Enhanced Biaxial Texture and Method of FabricatingSame by Goyal et al., issued Apr. 14, 1998; U.S. Pat. No. 5,741,377Structures Having Enhanced Biaxial Texture and Method of FabricatingSame by Goyal et al., issued Apr. 21, 1998; U.S. Pat. No. 5,898,020Structures Having Biaxial Texture and Method of Fabricating Same byGoyal et al., issued Apr. 27, 1999; U.S. Pat. No. 5,958,599 StructuresHaving Enhanced Biaxial Texture by Goyal et al., issued Sep. 28, 1999;U.S. Pat. No. 5,964,966 Method of Forming Biaxially Textured Substratesand Devices Thereon by Goyal et al., issued Oct. 21, 1999; and U.S. Pat.No. 5,968,877; High Tc YBCO Superconductor Deposited on BiaxiallyTextured Ni Substrate by Budai et al., issued Oct. 19, 1999,; U.S. Pat.No. 4,428,811 Rapid rate reactive sputtering of a group IVb metal bySproul et al., issued Jan. 31, 1984;

FIELD OF THE INVENTION

The present invention relates generally to epitaxial metal oxide filmsand, more particularly, to those films and related composite structuresas can be prepared by oxidizing a previously deposited nitride layer.

BACKGROUND OF THE INVENTION

Recent emergence of high-temperature superconducting (HTS) thick-filmtape technology is expected to meet the cost, size and performancerequirements of superconducting components needed for advanced powerapplications for the defense and commercial sectors. One of the majorpotential HTS applications is in the electric power industry.

The YBa₂Cu₃O₇ and related ceramic materials (YBCO) have appropriateintrinsic properties in the liquid nitrogen temperature range. However,their properties are drastically affected by grain boundarymisorientations. In order to provide high temperature and fieldapplications, it is imperative that a biaxially textured,polycrystalline YBCO tape, or related article, be developed whichcontains few high angle grain boundaries.

A biaxially textured, flexible metal/alloy substrate is formed byconventional thermomechanical processing followed by epitaxialdeposition of buffer layer(s), YBCO grown on such substrate oftenexhibited J_(c)'s over 1 MA/cm² at 77K. To date, the preferred bufferlayers have been the combination of CeO₂ and yttria stabilized zirconia(YSZ). However, these oxide buffer layers lack important properties,e.g., electrical and thermal conductivity and mechanical toughness. Ithas been a challenging engineering task to develop a large-scalecontinuous process for producing thick (>0.5 μm) crack-and pore-freeoxide films. Microcracking in oxide films is commonly observed in thickfilms due to the brittle nature of the oxide materials. Microcracks inthe oxide layer can serve as open paths for oxygen to diffuse andoxidize the underlying metal during subsequent YBCO processing. Finally,the oxide deposition step on the Ni substrates is difficult; highquality films are only obtained by using very low deposition rates. Inaddition, as with many HTS applications, conductive buffer layers areneeded since they would provide electrical coupling of the HTS layer tothe underlying metallic tape substrate. This is an important property inorder to electrically stabilize the conductor during transient loss ofsuperconductivity in some applications.

Conventional ceramic fabrication methods which can be used to make along, flexible conductor result in materials with weak, if any,macroscopic or microscopic biaxial texture. In particular, YBCOmaterials fabricated using conventional techniques invariably containnumerous high angle grain boundaries. High angle grain boundaries act asJosephson coupled weak-links leading to a significant field-dependentsuppression of the supercurrent across the boundary. For cleanstoichiometric boundaries, the grain boundary critical current densitydepends primarily on the grain boundary misorientation. The dependenceof J_(c)(gb) on misorientation angle was first determined by Dimos etal. in YBCO for grain boundary types that can be formed in epitaxialfilms on bicrystal substrates. These include [001] tilt, [100] tilt, and[100] twist boundaries. In each case high angle boundaries were found tobe weak-linked. The low J_(c) observed in randomly orientedpolycrystalline HTS fabricated using conventional methods can beunderstood on the basis that the population of tow angle boundaries issmall and that frequent high angle boundaries impede long-range currentflow. Hence, controlling the grain boundary misorientation distributiontowards low angles is key to fabricating high-J_(c) materials.

Successful fabrication of biaxially textured superconducting wire basedon the coated conductor technology, requires optimization of thecost/performance of the HTS conductor. From a superconductingperformance standpoint, a long, flexible, single crystal-like wire isrequired. From a cost and fabrication standpoint, an industriallyscalable, low cost process is required. Both of these criticalrequirements are met by Rolling-assisted-biaxially-textured-substrates.However, in order for cost/performance for a conductor based on thistechnology to be optimized, further work needs to be done in the area ofbuffer layer technology. It is now clear that while it is fairlystraight-forward to fabricate long lengths of biaxially textured metalsor alloys, it is quite difficult to deposit high quality buffer layersusing low cost processes. Requirements of buffer layers include—itshould provide an effective chemical barrier for diffusion ofdeleterious elements from the metal to the superconductor, provide agood structural transition to the superconductor, have a high degree ofcrystallinity, excellent epitaxy with the biaxially textured metaltemplate, have good mechanical properties, high electrical and thermalconductivity and should be able to be deposited at high rates.

Buffer layers of the prior art include use of YSZ and CeO₂, typically aconfiguration of CeO₂ (0.01 μm)/YSZ (0.5 μm)/CeO₂ (0.01 μm). The purposeof the first buffer layer is to provide a good epitaxial oxide layer onthe reactive, biaxially textured Ni substrate without the formation ofundesirable NiO. CeO₂ is special in its ability to very readily formsingle orientation cube-on-cube epitaxy on cube textured Ni. Depositionof CeO₂ using a range of deposition techniques is done using abackground of forming gas (4% H₂–96% Ar) in the presence of smallamounts of water vapor. Under such conditions the formation of NiO isthermodynamically unfavorable while the formation of CeO₂ isthermodynamically favorable. The water vapor provides the necessaryoxygen to form stoichiometric CeO₂. It is not possible to deposit YSZunder such conditions with no evidence of undesirable orientations. Inthe case of CeO₂ one can readily obtain a single orientation, sharp cubetexture. Ideally, it would be desired that the CeO₂ layer be grown thicksuch that it also provides a chemical diffusion barrier from Ni,followed by deposition of YBCO. However, when the CeO₂ layer is growngreater than 0.2 μm in thickness, it readily forms micro-cracks. Hence,an YSZ that does provide an excellent chemical barrier to diffusion ofNi and does not crack when grown thick is deposited on a thin initialtemplate of CeO₂. However, since there is a significant lattice mismatchbetween YSZ and YBCO (˜5%), a second 45°-rotated orientation nucleatesat times. In order to avoid the nucleation of this second orientationcompletely, a thin CeO₂ layer is typically deposited epitaxially on theYSZ layer, to complete the buffer layer structure. YBCO can now bedeposited on the layer that has an excellent lattice match with YBCO(˜0.1%).

The drawbacks of this buffer layer structure are that the deposition ofthe first CeO₂ layer is non-trivial. Strict control of depositionconditions in particular, the O₂ partial pressure is required to avoidformation of undesirable NiO (NiO typically nucleates in mixedorientations and is also very brittle). Furthermore, CeO₂ can have widerange of oxygen stoichiometries. It is brittle and is not conducting. Itwill be a challenging engineering task to develop a large-scalecontinuous process for producing thick (>0.5 μm) crack-and porosity-freeoxide films. For example, in a continuous process involving reactiveelectron beam evaporation of Ce to form CeO₂, issues relating to theformation of an oxide on the target complicate matters relating to rateof deposition as well as stability of the melt pool. Any change ofconditions during deposition is known to have profound affects on thefilm microstructure. Moreover, any oxidation of the biaxially texturedmetal, even after the successful deposition of CeO₂, can induceundesirable interfacial stresses leading to spallation or furthercracking, thus deteriorating the material properties. Microcracks in theoxide buffer layer will adversely affect the epitaxial quality of thegrowing YBCO film and create weak-links, besides serving as diffusionpaths for Ni. Lastly, the surface morphology of the buffer layer isimportant for subsequent YBCO growth. Ideally, it would be desired tohave a buffer layer which tends to be smoother than the Ni substrate itis grown on. All things considered, buffer layer deposition of the priorart is time-consuming and qualitatively deficient.

It has been an on-going concern in the art to meet the increasingdemands for improved performance and miniaturization in next generationof electronic devices and components. New and advancedmaterials—primarily in the form of thin films—will be required.Deposition of oxide thin films is being pursued for a number ofelectronic applications including microelectronics (memory andmicroprocessing), sensors, fuel cells, superconductors, photonics, andother specialty markets. Oxide films provide protection against chemicalattack, electrical and thermal insulation, and suitable dielectricproperties, etc. However, as mentioned above, primary technical barriersin processing of oxide films include low deposition rates, poor filmquality, and oxidation of substrate surfaces during deposition.

One approach to the aforementioned concerns has been to depositalternate materials on the substrate to alleviate the mechanicaldeficiencies of the prior art oxides. Such materials are more robust,but often exhibit a lattice mismatch significantly detrimental to laterdeposition of a functional electromagnetic layer. Invariably, this andrelated difficulties are addressed with use of one or more suitableoxide layers. However, many of the aforementioned problems inherent tooxide films—slow deposition rates and micro-cracking, among them—remainand impede efficient, cost-effective buffer formation and devicefabrication.

To illustrate, consider Lee, et al., Formation and Characterization ofEpitaxial TiO₂ and BaTiO₃/TiO₂ Films on Si Substrate. Jpn. J. Appl.Phys. Vol. 24, Pt. 1, No. 2B (February, 1995). Titanium dioxide thinfilms are described as converted from a nitride precursor. However, theresulting oxide is not biaxially textured; it is epitaxial out of planebut not in plane as would be necessary for superconducting applications.Biaxial texture can be defined in the context of superconductingapplications as having a full-width—half-maximum (FWHM) less than about15°, and preferably below 10°, for both in-plane and out of planeorientations. Further, the Lee films are described as having a rutilephase, presumably without an epitaxial lattice match as evidenced byx-ray results. The films are rough and porous, and exhibit high leakageand poor dielectric properties. Even so, there is no indication thatthis system could be extended, if desired, to deposit other materials onsubstrates more suitable to superconductor applications.

The foregoing background information, together with other aspects of theprior art, are disclosed more fully and better understood in light ofthe following publications:

-   1. Kormann, G., Bilde, J. B., Sorensen, K., de Reus, R., Anderson R.    H., Vace, P., and Freltoft, T., “Relation between Critical Current    Densities and epitaxy of Y-123 Thin Films on MgO (100) and SrTiO₃    (100),” J. Appl. Phys., 1992, 71, 3419–3426.-   2. Matsuda, H., Soeta, A., Doi, T., Aikhara, and T. Kamo,    “Magnetization and Anisotropy in Single Crystals of Tl-1223 of    Tl—Sr—Ca—Cu—O System,” Jpn. J. Appl. Phys., 1992, 31, L1229–31.-   3. Dimos, D., Chaudhari, P., Mannhart, J., and F. K. LeGoues,    “Orientation Dependence of Grain Boundary Critical Currents in    YBa₂Cu₃O_(x) Bicrystals”, Phys. Rev. Lett., 1988, 61, 219–222;    Dimos, D., Chaudhari, P., and Mannhart, J., “Superconducting    Transport Properties of Grain-boundaries in YBa₂Cu₃O_(x)    Bicrystals”, Phys. Rev. B, 1990, 41, 4038–4049.-   4. Iijima, Y., Tanabe, N., Kohno, O., and Ikeno, Y., “In-plane    Aligned YBa₂Cu₃O_(x) Thin-Films Deposited on Polycrystalline    Metallic Substrates”, Appl. Phys. Lett., 1992, 60, 769–771.-   5. Reade, R. P., Burdahl, P., Russo, R. E., and Garrison, S. M.,    “Laser Deposition of Biaxially Textured Yttria-stabilized Zirconia    Buffer Layers on Polycrystalline Metallic Alloys for High Critical    Current Y—Ba—Cu—O Thin-films”, Appl. Phys. Lett., 61, 2231–2233,    1992.-   6. Wu, X. D., Foltyn, S. R., Arendt, P. N., Blumenthal, W. R.,    Campbell, I. H., Cotton, J. D., Coulter, J. Y., Hults, W. L.,    Maley, M. P., Safar, H. F., and Smith, J. L., “Properties of    YBa₂Cu₃O_(x) Thick Films on Flexible Buffered Metallic Substrates”,    Appl. Phys. Lett., 1995, 67, 2397.-   7. Hasegawa, K., Fujino, K., Mukai, H., Konishi, M., Hayashi, K.,    Sato, K., Honjo, S., Satao, Y., Ishii, H., and Iwata, Y., “Biaxially    Aligned YBCO Film Tapes Fabricated by All Pulsed Laser Deposition”,    Appl. Supercond., 4, 475–486, 1996.-   8. Goyal, A., Norton, D. P., Christen, D. K., Specht, E. D.,    Paranthaman, M., Kroeger, D. M., D. P., Budai, J. D., He, Q.,    List, F. A., Feenstra, R., Kerchner, H. R., Lee, D. F., Hatfield,    E., Martin, P. M., Mathis, J., and Park, C., “Epitaxial    Superconductors on Rolling-Assisted-Biaxially-Textured-Substrates    (RABiTS): A Route Towards high Critical Current Density Wire”,    Applied Supercond., 1996, 69, 403–427.; A. Goyal et al., U.S. Pat.    No. 5,739,086 and U.S. Pat. No. 5,741,377.-   9. Norton, D. P., Goyal, A., Budai, J. D., Christen, D. K.,    Kroeger, D. M., Specht, E. D., He, Q., Saffian, B., Paranthaman, M.,    Klabunde, C. E., Lee, D. F., Sales, B. C., and List, F. A.,    “Epitaxial YBa₂Cu₃O_(x) on Biaxially Textured Nickel (100): An    Approach to Superconducting Tapes with High Critical current    Density”, Science, 1996, 274, 755.-   10. Goyal, A., Norton, D. P., Kroeger, D. M., Christen, D. K.,    Paranthaman, M., Specht, E. D., Budai, J. D., He, Q., Saffian, B.,    List, F. A., Lee, D. F., Hatfield, E., Martin, P. M., Klabunde, C.    E., Mathis, J., and Park, C., “Conductors With Controlled Grain    Boundaries: An Approach To The Next Generation, High Temperature    Superconducting Wire”, J. Mater. Res., 1997, 12, 2924–2940.-   11. Goyal, A., Norton, D. P., Budai, J. D., Paranthaman, M.,    Specht, E. D., Kroeger, D. M., Christen, D. K., He, Q., Saffian, B.,    List, F. A., Lee, D. F., Martin, P. M., Klabunde, C. E., Hatfield,    E., and Sikka, V. K., “High Critical Current Density Superconducting    Tapes By Epitaxial Deposition of YBa₂Cu₃O_(x) Thick Films on    Biaxially Textured Metals”, Appl. Phys. Lett., 1996, 69, 1795.-   12. W. D. Sproul, “Physics and Chemistry of Protective Coatings”,    Ed. by W. D. Sproul, J. E. Greene, and J. A. Thornton (AIP Conf.    Proc. No. 149, 1986, New York), p. 157.

OBJECTS OF THE INVENTION

There are numerous problems related to the prior art as pertains to theuse and deposition of oxide layers on metal/alloy substrates. Thus thereis a need for a new approach to buffer configuration and incorporationof various oxide materials. There is also a corresponding need for thefabrication of such materials/layers at high rates without prematuresubstrate oxidation. Accordingly, it is one object of the presentinvention to provide a new, commercially-viable and easily scalablemethod for the high-rate formation of epitaxial oxide layers. It will beunderstood by those skilled in the art that one or more aspects of thisinvention can meet certain objectives, while one or more other aspectscan meet certain other objectives. Each objective may not apply equally,in all instances, to every aspect of the present invention. As such, thepresent objects can be viewed in the alternative with respect to any oneaspect of the present invention.

It is another object of the invention to provide an epitaxial nitridelayer and, thereafter, the nitride layer converted to an epitaxial oxidelayer.

It is yet another object of the invention to provide a method forobtaining good quality epitaxial oxides without premature substrateoxidation.

It is yet another object of the present invention to provide for the useof the epitaxial oxide layers converted from epitaxial nitride layers astemplates to grow epitaxial metal/alloy/ceramic and/or device layers.

It is yet another object of this invention to provide an epitaxialnitride layer and methods for subsequent conversion thereof to an oxideproviding a sufficient lattice match for later deposition of afunctional electromagnetic layer. More specifically, it can also be anobject of this invention, alone or in conjunction with other suchobjects, to provide one or more oxide layers having cubic crystallinemorphology with an epitaxy sufficient for subsequent deposition of afunctional electromagnetic material. Such objects can also be achievedthrough use of the present invention in conjunction with substratessuitably textured for functional applications of the sort describedherein.

It is yet another object of the present invention to provide for the useof a nitride as a protective layer on a metal or alloy or ceramicsubstrate whereby long lengths of metal tape or wire can be spooled orotherwise configured until it is converted to an epitaxial oxide,partially or entirely just prior to subsequent oxide layer growth.

It is yet another object of the present invention to provide a methodfor the fabrication of oxide thin films on or in conjunction withsuitable substrates, such films as can be used as part of a composite ina variety of electronic devices, including but not limited tosuperconducting tapes and/or wires.

Other objects, features, benefits and advantages of the presentinvention will be apparent from the foregoing in light of the followingsummary and descriptions, and will be readily apparent to those skilledin the art have a knowledge of various buffer layers, composites,articles and their methods of manufacture. Such objects, features,benefits and advantages will be apparent from the above as taken inconjunction with the accompanying examples, figures, tables, data andall reasonable inferences to be drawn therefrom.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method ofpreparing a epitaxial article is presented and includes providing asubstrate, having a biaxial texture or a random orientation, having asurface and depositing onto the surface, in the presence of nitrogengas, an epitaxial layer of a nitride; and further oxidizing theepitaxial nitride layer to form an epitaxial oxide layer in the presenceof an oxidizing agent. The oxidation step can be performed eitherin-situ or can be annealed externally in oxidizing atmospheres.

In accordance with still a further aspect of the present invention, amethod of preparing an epitaxial article includes providing a biaxiallytextured substrate having a surface and depositing onto the surface, anepitaxial layer of a nitride; and further oxidizing the epitaxialnitride layer to form an epitaxial oxide layer; and further depositingon the epitaxial oxide layer a second epitaxial layer of an oxide suchas but not limited to MgO, CeO₂,YSZ, BaPbO₃, LaAlO₃, SrTiO₃, LaNiO₃,Y₂O₃, and/or RE₂O₃ (where RE is an acronym for any of the rare earthmetals); and, optionally, further depositing on the oxide layer anadditional electromagnetic/optical epitaxial device layer such as butnot limited to a superconducting layer. Without limitation, reference ismade to the results and data of Examples 15–16, below.

In accordance with another aspect of the present invention, epitaxialnitride layers can be deposited at high rates using a technique such asreactive magnetron sputtering with metal targets under nitrogencontaining atmosphere, or magnetron sputtering with nitride targets.Reactive magnetron sputtering provides high deposition rates approachingthose available using metal sputtering techniques.

In accordance with another aspect of the present invention, epitaxialnitride layers can be deposited on biaxially textured substrates by amultiple-deposition-temperature technique to accommodate the relativelylarge lattice match between the nitride and substrate. The initialdeposition is done at lower temperature to suppress island growth whilehigher temperature is used for the rest of deposition.

In accordance with one aspect of the present invention, the foregoingand other objects can be illustrated with a biaxially textured articlewhich includes a biaxially textured substrate having thereon anepitaxial layer of a novel nitride composition, a yttrium zirconiumnitride (YZN).

In accordance with yet another aspect of the present invention, theforegoing and other objects can be demonstrated with a biaxiallytextured article which includes a biaxially textured substrate havingthereon an epitaxial YSZ layer converted from YZN, having thereon,optionally, an epitaxial layer of an oxide such as but not limited toMgO, CeO₂, YSZ, LaAlO₃, SrTiO₃, BaPbO₃, LaNiO₃, Y₂O₃, and/or RE₂O₃, andas a further option an additional electromagnetic/optical, epitaxialdevice layer such as a superconducting layer.

In accordance with yet another aspect of the present invention, theforegoing and other objects can be met by a biaxially textured articleor device which includes a biaxially textured substrate initially havingthereon an epitaxial nitride layer, subsequently converted to an oxidesuch as but not limited to CeO₂, YSZ, LaAlO₃, SrTiO₃, Y₂O₃, and/orRE₂O₃, and as a further option including an additionalelectromagnetic/optical, epitaxial device layer such as asuperconducting layer.

In part, the present invention is a method of preparing an oxide film,preferably, one that affords epitaxial coverage. The method includes (1)providing a substrate surface; (2) placing a nitride composition layeron the substrate surface, the nitride composition including but notlimited to transition and rare earth metal compounds and combinationsthereof; and (3) oxidizing the nitride composition to provide thedesired oxide film. In preferred embodiments, the nitride composition isannealed. The conversion is at a time and temperature sufficient toprovide complete oxidation of the nitride layer. However, as describedelsewhere herein, conversion may be controlled so as to provide apartially-oxidized nitride layer, as may be desired for a particular enduse application. Regardless, conversion can be accomplished using oxygengas as the oxidizing agent, with the rate and extent of oxidation as canbe controlled by the oxygen partial pressure. Other oxidizing agents canalso be used according to straight-forward modifications of thepreparatory techniques described herein, such agents including but notlimited to water, ozone, a suitable peroxide, and metal-organic oxygensources.

The nitride layers of this invention can be placed and/or deposited on avariety of suitable substrate materials, including biaxially-texturedsubstrate or those metal and/or alloy materials without specificorientation. Such placement can be accomplished by processes well-knownto those skilled in the art, using, in particular, those techniquesdescribed below or as can be ascertained from modification of thetechnologies set forth in the aforementioned incorporated references.For instance, for the reactive magnetron sputtering device, such as thatschematically represented in FIG. 14, can be used with either nitride orcarbide targets, or corresponding metal targets under a nitrogencontaining atmosphere. Such devices and their operation, along withsimilar deposition techniques, are well-known, understood, and would beavailable to those individuals made aware of this invention. Epitaxialprecursor placement and/or growth can be achieved sequentially over atemperature range, the bounds of which vary with the chemical identityof the precursor material. While a two temperature sequence is shownbelow, other multiple temperature increments can be used with comparableeffects for precursors with or without solute/dopant additives.

As described below, nitride placement/deposition can be moretime-efficient than those related methods of the prior art. Reactivesputtering of the type described herein, is a relatively rapid process,with rates that can approach about 1 μm/min through use of apparatus andequipment now available with straight-forward modifications as would beunderstood by those skilled in the art made aware of this invention.Such layers provide a buffer between the substrate material andelectromagnetic layer or film subsequently deposited thereon. Thenitride layers of this invention, prior to oxidation, are mechanicallyrobust and have high electrical and thermal conductivities. Thosemechanical properties can be exploited, as described more fully below.The associated conductivities provide good electrical and thermalcontact, as would be required in a variety of integrated deviceapplications. Such nitrides, and carbides, are available eithercommercially or synthetically as the corresponding transition,lanthanide and rare earth metal compounds or combinations thereof.Epitaxial substrate coverage can be obtained, as described below.Stoichiometric control allows tailoring of the nitride/carbide latticeparameters so as to provide a good buffer between the substrate and thedesired electromagnetic/integrative layer.

Conversion of a precursor nitride composition to an oxide film can be,as described below, achieved in situ immediately after nitridedeposition on the substrate surface. However, a unique advantage of thisinvention allows for whole or partial conversion at a time and place farremoved from the point of nitride deposition. As described below,oxidation ex situ is possible given the beneficial structural propertiesexhibited by the nitride precursor. Such a composite, device ormanufactured article can be configured for storage or shipment withoutcompromising epitaxial coverage. The nitride can be oxidized just priorto subsequent fabrication, such as deposition of a superconducting orother such ceramic material en route to the desired integrated device.Reference is made to FIG. 16, the representative parameters providedtherein, in conjunction with the following descriptions and examples.

Various embodiments of the present invention include multiple nitridelayers, any one or all of which can be oxidized in situ depending upon aparticular end use application. Any remaining nitride precursor can beoxidized ex situ. Even so, a preferred embodiment of this inventionrelates to deposition of one zirconium nitride composition, optionallyincluding a solute or dopant at a concentration required to furtherenhance the stability of the resulting oxide structure. As with otherembodiments, useful additives include yttrium nitride, as well as othersuch materials capable of forming a solid solution with the nitride.Regardless, the enhanced stability imparted by the solute permits, ifnecessary, later oxidation ex situ to provide an oxide film on which canbe deposited additional material layers.

Implicit from the foregoing discussion, the present invention alsoincludes use of a precursor composition to prepare an epitaxial oxidefilm. The method of preparation includes (1) deposition of an epitaxialprecursor film on a substrate surface or another film or layerpreviously deposited on the substrate, with the precursor compositionsincluding but not limited to transition and rare earth metal nitrides,carbides, and combinations thereof; and (2) conversion of the precursorcomposition to an epitaxial oxide film, with the thickness thereof ascan be determined by parameters relating to conversion of the precursorcomposition. Where the precursor composition is deposited on apreexisting nitride or carbide layer,-subsequent conversion can also,alternatively, oxidize one or more of the preexisting layers. Partialoxidation can be useful, depending upon end use application, where theprecursor material is a nitride composition. However, a carbideprecursor typically requires complete conversion to the oxide forreasons relating to subsequent fabrication. For instance, residualcarbon can contaminate and interfere with the function of a ceramicsuperconducting material applied thereafter.

As can be inferred from the foregoing, the present invention alsoincludes a composite having a metal oxide layer on a metal substrate,with the oxide layer produced and/or obtainable from the oxidation of ametal nitride composition previously deposited on the substrate. Theoxide layer can be characterized as having a substantially singleepitaxial orientation. Preferred embodiments provide an oxide layersubstantially without a nitride component; however, partial oxidation ofthe previously-deposited metal nitride can provide a residual nitridecomponent, as demonstrated by one or more of the following examples.Regardless, such preferred metal oxides are stabilized with a dopant. Inhighly preferred embodiments, the composite includes a yttria stabilizedzirconia composition on a biaxially textured metal/alloy substrate.

In part, the present invention also includes one or more functionallyintegrated devices, such devices having, without limitation, dielectric,refractory, ferro-electric, electro-optical, non-linear optical, fieldemission, photonic, waveguide, semi-conducting and/or super-conductingapplications, such devices as could be fabricated using the presentinvention in conjunction with other techniques and components known tothose skilled in the art. Such integrated devices include a compositestructure having a substrate and at least one epitaxial nitridecomposition deposited thereon, with the nitride compositionpartially-oxidized as described elsewhere herein. In preferredembodiments, the composite also includes an electromagnetic filmproviding a desired functionality to the integrated device. In variouspreferred embodiments, the partially oxidized nitride composition is thereaction product of an yttrium zirconium nitride and a suitableoxidizing agent. The partial-oxidation characteristics of such acomposition can be utilized and maintained under reducing conditions,such as would be utilized in the fabrication of a ferro-electric device.

In part, the present invention is also a configured composite includinga substrate material, biaxially textured or having another suitableorientation, and at least one nitride layer thereon. In preferredembodiments, a nitride layer is epitaxial. Taking advantage of themechanical stability afforded through use of such nitride buffer layers,the inventive composite can be arranged about an axis perpendicular tothe configuration, such an arrangement as can be provided with thecomposite coiled around and about a spool. Such a configuration ispossible through use of the nitride compositions described herein andallows for the storage, transportation and/or later fabrication of thesubject composite.

Preferred embodiments of the composites, structures and/or devicesdescribed herein can include a novel composition of matter: a solidsolution of zirconium nitride and yttrium nitride represented by theformula (Zr_(x)Y_(1−x))N, where x is a value from about 0.1 to about0.9. While various stoichiometries are available and can be used goodeffect, preferred solutions are those in which the value of x is about0.6 to about 0.9.

As mentioned above, the present invention teaches a unique way toproduce epitaxial oxide films via first depositing a nitride film atvery high rates and then converting it into an oxide by a post annealingstep under controlled partial pressure of oxidizing atmospheres. In oneexample of the present invention, YZN (as intimated above, YZN refers toZrN doped with varying contents of YN) films with a molar ratio ofY(0.2)/Zr(0.8) can be developed then subsequently converted to YSZcontaining 10 mole % yttria. The identification of a YZN compositionsuitable for conversion to YSZ is not trivial, because the solubility ofYN with ZrN should provide a stable YZN composition. As is shown in oneexample of the present invention, YZN film with a molar ratio of 50% YNand 50% ZrN exhibited phase separation to YN and ZrN at relatively highgrowth temperature. The amount of yttrium (or yttria) in YSZ affects thestability of the cubic phase, and this invention includes a range ofyttria concentrations required to achieve the desired YSZ phasestability. Stabilized cubic zirconia can also be formed withdopants/additives other than yttria, so long as those stabilizingelements are sufficiently soluble with the nitride precursor.Appropriate oxidation and/or conversion conditions are then employed toform YSZ epitaxially on YZN.

Without restriction to any one theory, mode or mechanism, it is thoughtthat similar cubic symmetries together with a reasonably small latticemismatch allow formation of an epitaxial oxide film on the nitridesurface as nitrogen is released into the atmosphere and oxygen isincorporated in the compositional structure. Regardless, epitaxy isachieved at high rates without premature substrate oxidation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a XRD θ-2θ scan from a Y_(0.2)Z_(0.8)N film grown on Ni(001) using high-rate reactive sputtering, showing only (002)reflections. FIG. 1 inset also compares the rocking curve from YZN (200)and Ni (200), showing the FWHM of ˜3.4° and 5.5° for YZN and Ni,respectively. Note that the FWHM of YZN is almost 2° smaller than thatof Ni, indicating out-of-plane texture and smooth surface morphologysubstantially better than that of Ni.

FIG. 2 compares the phi-scan from (a) YZN (111) and (b) Ni (111). TheFWHM of the phi-scan peaks were ˜10.5° and ˜8.2° for YZN and Ni,respectively. Only a single orientation, corresponding to thecube-on-cube epitaxy of YZN on the biaxially textured Ni is evident.

FIG. 3 shows XRD θ-2θ scan from 50 nm thick magnetron sputteredY_(0.2)Zr_(0.8)N (YZN) grown at constant temperature of ˜550° C. Thepattern shows an intense (200) peak but a small (111) peak. Thisindicates that while this sample has substantial out of plane texture in(200) direction, but is not epitaxial. The rocking curves (theout-of-plane texture) of the YZN layer was found to be ˜5.8° in therolling direction.

FIG. 4 shows the (111) phi-scan from same sample as in FIG. 1. Thelocation of the peaks in the (111) phi scan are consistent with acube-on-cube epitaxial relationship. The YZN (111) phi scan showed afull-width-half-maximum (FWHM) obtained by fitting a Gaussian curve tothe data to be ˜10.9°, indicating the grains that aligned to (200)orientation in out-of-plane direction also has some in-plane textures.

FIG. 5 shows θ-2θ x-ray diffraction (XRD) scan of a nominalY_(0.5)Z_(0.5)N film grown on MgO. The thickness of film was ˜500 nm.The pattern clearly shows presence of both YN and ZrN phases suggestinga phase miscibility gap existing in the YN—ZrN pseudo-binary system atsuch growth temperatures.

FIG. 6 shows a θ-2θ scan from a YSZ film formed by oxidation of a YZNfilm grown on Ni (001) using high-rate reactive sputtering, showing only(002) reflections. The YZN sample used was showed XRD peak as isillustrated in FIG. 3. FIG. 5 inset also compares the rocking curve fromYSZ (200) and Ni (200), showing the FWHM of ˜4.8° and ˜5.5° for YSZ andNi, respectively. FWHM of YZN is 0.7° smaller than that of Ni,indicating out-of-plane texture and smooth surface morphology betterthan that of Ni.

FIG. 7 compares the phi-scan from YSZ (111). The FWHM of the phi-scanpeaks were ˜11.0°. Only a single orientation, corresponding to thecube-on-cube epitaxy of YSZ on the biaxially textured Ni is evident.Notice that the FWHM value of YSZ (111) is close to that of YZN (111) inFIG. 4 in spite of large lattice mismatch between YSZ and YZN (11.2%).

FIG. 8 shows a high magnification scanning electron micrograph of thesurface of YZN deposited epitaxially on biaxially textured Ni. Noevidence of any microcracks can be seen.

FIG. 9 shows a high magnification scanning electron micrograph of thesurface of YSZ converted from YZN sample deposited epitaxially onbiaxially textured Ni. No evidence of any microcracks can be seen.

FIG. 10 θ-2θ XRD scan from YBCO coated YSZ (100 nm)/Ni samples. Insetcompares rocking curve from YBCO (005) and YSZ (200).

FIG. 11 shows a YBCO (103) pole figure for a YBCO/converted YSZ/Nisample. Only a single orientation, corresponding to the cube-on-cubeepitaxy of YSZ on the biaxially textured Ni is evident.

FIG. 12 shows phi-scan of YBCO (103) from YBCO/converted YSZ/Ni sample,The FWHM value was 15°. The value for YBCO is typically consistent withhigh J_(c) values.

FIG. 13( a) is a θ-2θ x-ray diffraction (XRD) scan of a typical film,showing only YZN (002) and YSZ (002) peak from as oxidized YZN films.The off-axis phi-scan of the TiN (220) and YSZ (220) peaks shown inFIGS. 13( b) and (c) respectively, verifies the cube-on-cube epitaxialorientation of YSZ on YZN.

FIG. 14 is a schematic representation of a UHV reactive magnetronsputtering chamber of the type useful with the method(s) of thisinvention.

FIG. 15 illustrates schematically a wound and/or spooled compositeconfiguration, such composite as can be configured in accordance withthe preparation and/or manufacturing methods described herein. Forpurposes of illustration, only, the composite tape, including YZN orother nitrides of this invention, can be wound on a spool/reel toprovide curved configurations varying with the dimensions thereof(e.g.—spooled radii from 1–12 inches).

FIG. 16 provides a schematic depiction of several thin filmfabrications, each of which is in accordance with the present invention,but only illustrative of the methods provided elsewhere herein.

FIG. 17 shows three, (a)–(c), XRD scans as more fully discussed inExample 14.

FIG. 18 is a cross-section TEM bright field micrograph image fromYSZ/YZN/Si sample. The YSZ and YZN layers are clearly distinguished,with a thickness of 70 and 130 nm, respectively. Both YSZ and YZN layershave a columnar structure and the YSZ/YZN interface appears well-definedand relatively flat and smooth. There is no indication or formation ofsignificant intermediate phase in the interface.

FIG. 19 is a high-resolution cross-section TEM bright field imageshowing atomic planes near YSZ/YZN interface. The YSZ (111) atomic planeruns from top to interface region continuously and continue to YZN (111)plane. The interface is sharp and appears to be locally coherent insinge grains, clearly indicating that there are no intermediate phasepresent near the interface, as would be advantageous for process controland device design as well as for improved performance of such deviceslike oxygen sensors.

FIG. 20 is a phi scan of Ni (111) showing FWHM ˜9.22°; see Example 15.

FIG. 21 is a phi scan of YSZ (111) showing FWHM ˜10.04°; see Example 15.

FIG. 22 is a phi scan of CeO₂ (111) showing FWHM ˜9.52°; see Example 15.

FIG. 23 is a phi scan of YBCO (111) showing FWHM ˜9.52°; see Example 16.

FIG. 24 shows J_(c) measurement on 250 nm thick YBCO grown onCeria/ATFI-YSZ/Ni corresponding to a calculated J_(c) value ˜1.0×10⁶A/cm² at 77K by whole body transport current measurement in self-fieldusing a 1 μv/cm criteria; see Example 16.

FIG. 25 shows a XRD θ-2θ scan from a YZN film grown on Ni—Cr (13%) (001)using high-rate reactive sputtering, showing only (002) reflections.FIG. 25 inset also compares the rocking curve from YZN (200) and Ni—Cr(13%) (200), showing the FWHM of ˜4.2° and 5.8°° for YZN and Ni—Cr(13%), respectively. FWHM of YZN is almost 2° smaller than that of Ni,indicating out-of-plane texture and smooth surface morphologysubstantially better than that of Ni.

FIG. 26 compares the phi-scan from (a) YZN (111) and (b) Ni—Cr (13%)(111). The FWHM of the phi-scan peaks were ˜10.6° and ˜7.2° for YZN andNi, respectively. Only a single orientation, corresponding to thecube-on-cube epitaxy of YZN on the biaxially textured Ni is evident.

FIG. 27 shows a θ-2θ scan from a YSZ film formed by oxidation of a YSZfilm grown on Ni—Cr (13%) (001) using high-rate reactive sputtering,showing only (002) reflections. Inset in FIG. 27 also compares therocking curve from YSZ (200) and Ni—Cr (13%) (200), showing the FWHM of4.8°. FWHM of YSZ is 1.9° smaller than that of Ni—Cr, indicatingout-of-plane texture and smooth surface morphology better than that ofNi.

FIG. 28 compares the phi-scan from YSZ (111). The FWHM of the phi-scanpeaks were ˜11.8° and ˜7.2°. Only a single orientation, corresponding tothe cube-on-cube epitaxy of YSZ on the biaxially textured Ni is evident.

FIG. 29( a) provides θ-2θ x-ray diffraction (XRD) scan of a typical YZN(40 nm)/ZrN (20 nm)/Si (001) structure. Inset shows a rocking curve ofnitride (002); (b) The off-axis phi scans of the nitride (111).

FIG. 30 shows a cross-sectional TEM micrograph of a grown Si/YZN/YSZsample.

FIG. 31 provides a nitrogen map from the same area as FIG. 30. Insetshows integrated intensity profile across the interface.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new methodology for preparing epitaxialmetal oxide layers from epitaxial nitride layers under controlledoxidation conditions. Epitaxial nitrides can be deposited at high rateson highly lattice mismatched biaxially textured metal substrates priorto oxidation. Accordingly, a new composition of matter, (ZrY)N, has alsobeen developed that can be converted to YSZ.

As mentioned above, in deposition of epitaxial oxide layers for variousapplications, there are a number of problems due to premature oxidationof substrate. For example, initial oxide buffer layer deposition onbiaxially textured Ni/Ni alloy substrate for YBCO superconductor devicesare problematic due to NiO formation. Available techniques for epitaxialoxide layer growth on Ni/Ni-Alloy substrates are slow and difficult tocontrol. Direct oxide deposition is only feasible by first depositingCeO₂ under reduced conditions prior to growth of a relatively thick YSZlayer. Thus, high quality epitaxial YSZ layers cannot be grown directlyon these substrates. The present invention allows for formation of YSZthrough conversion of YZN, thus avoiding an extra step of ceriadeposition. While methods for producing biaxially textured substratesand subsequently depositing of YBCO were taught in previous U.S. Pat.Nos. 5,739,086, 5,741,377, 5,898,020, 5,958,599, 5,739,086, 5,741,377,5,898,020, and 5,958,599, by Goyal et al., and U.S. Pat. No. 5,968,877by Budai et al., these inventions did not teach the fabrication ofscalable oxide buffer layers with high growth rates.

The present invention allows high rate formation of epitaxial oxideswith high deposition rate and without the undesired oxidation ofsubstrate. Because the oxidation proceeds in a direction fromnitride/atmosphere interface toward nitride/substrate interface, epitaxyquality is not effected by substrate oxidation. Oxide thickness can becontrolled because the conversion rate depends on the diffusion rate ofoxygen (or progressive action of another such oxidizing agent).

The present invention also includes use of various other oxidizingagents—depending on the chemical properties of nitride, oxide andsubstrate—such agents including, but not limited to oxygen, water,ozone, suitable peroxide or metal-organic oxygen sources. For example,an epitaxial YZN layer was converted to epitaxial YSZ under high purityhydrogen atmosphere containing controlled amount of water. The oxygenpartial pressure is dictated by and annealing temperature/water partialpressure and it can be controlled to be <10⁻²⁰ atmosphere. Ni substratesare resistant to oxidation under such conditions, but YZN oxidizesrelatively quickly to YSZ, forming an epitaxial YSZ layer withoutsubstrate contamination.

Another aspect of this invention is that upon oxidation, converted oxideshows no significant deterioration in biaxial texture compared to theprecursor nitride film, even at high the rate of oxidation. As is shownin FIG. 4, the FWHM of (111) phi-scan from YSZ shows less than 1 degreedifference from that of (111) phi-scan from YZN, indicating that thebiaxial texture of YSZ is comparable to that of the precursor nitride,YZN, despite a 11% lattice mismatch. The out-of-plane rocking curve dataof FIG. 5 for YSZ shows less than a degree difference compared to therocking curve data for YZN in FIG. 3.

The present invention also provides a way of exploiting unique nitrideproperties to facilitate the related manufacturing processes. Forexample, manufacturing YBCO coated conductor wire requires multiplesteps of spooling and winding, each of which poses mechanical stresseson the ceramic films or substrate. One can convert YZN to YSZ just priorto growth of YBCO, so that spooling/winding can be done with YZN on asubstrate rather than the mechanically weaker YSZ. It is, therefore,possible and advantageous to avoid buffer cracking and spalling suchthat high quality functional films, such as YBCO, can be grown on YSZ.

Multiple layers of different nitrides can be deposited with high ratesand converted to oxide sequentially, if such a configuration is requiredfor a specific application—depending on structural,electro-magmentic/optical, mechanical or thermal properties of oxide andnitride. For example, a thin ZrN layer can be deposited on a substrateto improve the epitaxial quality/in-plane orientation of a YZN filmdeposited thereon. See, for instance, Example 15. As a further example,a thin epitaxial TiN layer can be first deposited on Ni substrate,rather than YZN, because it has smaller lattice mismatch with Ni (19%)than YZN (31%) and allows for more straightforward growth process. Athick YZN layer can then be deposited on TiN-coated Ni or other metal ormetal alloy substrates, relatively easily due to the smaller mismatchbetween YZN and TiN (˜10%). Subsequent oxidative conversion produces anepitaxial TiO_(x)/YSZ composite on Ni. Epitaxial nitrides can also bedeposited on biaxially textured metal/alloy substrates at high rateseven when a large lattice mismatch between nitride and substrate ispresent.

A method of depositing metal nitride by high rate using magnetronsputtering is described in U.S. Pat. No. 4,428,811 which is incorporatedherein by reference in its entirety. Both reactive and inert gases areadmitted to the sputtering chamber. The flows were controlled in such away that the deposition rate of sputtering is not significantly loweredthan that of pure metal. The amount of the reactive gas is constantlysampled to provide a control signal used to regulate admission of thereactive gas at the proper rate for most effective deposition of themetal onto the substrate. Closed loop systems regulate the level ofelectrical power supplied to the target, rate of admission of the inertgas, and rate of admission of the reactive gas. Such a system can beutilized in conjunction with the present invention.

While, a typical growth of an epitaxial layer uses a constant growthtemperature throughout the deposition, epitaxial YZN layers aretypically deposited on biaxially textured substrates such as Ni andNi-alloy using a two-step deposition procedure—where initial growth ofYZN is done at a relatively lower temperature. Unlike other transitionmetal nitrides such and TiN and VN, which show relatively smallerlattice mismatch with Ni (TiN 19%, VN 18%), deposition of YZN under aconstant growth temperature is not entirely successful due to very largelattice mismatch between YZN and Ni (31%).

It is observed that the oxidation process can be kinetically controlledby adjusting a parameter such as partial pressure of oxygen and/ortemperature. Such control is important for obtaining smooth, crack-freeoxide layers without defects associated with the conversion, i.e.,spalling, cracking or bubbles due to gas elements trapped in layers. Forexample, epitaxial YSZ converted at 800° C. under water vapor with apartial pressure of ˜0.03 atmosphere resulted in layer spallation and,gas bubble formation on oxide layer, while the X-ray characterizationstill showed a good biaxial texture. However, when the same conversionwas done under water partial pressure of ˜10⁻⁶ atmosphere, the YSZsurface showed no evidence of spalling, microcracking or gas bubbles.

The nitrides of the present invention can be oxidized in situ, (inplace; e.g., within a nitride deposition chamber), or ex situ as laterperformed in a conventional furnace under conversion conditions ifadvantageous due to chemical, physical properties of a specificnitride/oxide. For example, because YBCO possess smaller latticemismatch with CeO₂ (<0.1%) than with YSZ, thus may be desirable to capthe YSZ/Ni with CeO₂ for easier epitaxial YBCO process. One way toaccomplish this would be deposit a thin CeN layer on top of the YZNlayer, then convert it to the corresponding oxide. However, it is knownthat the CeN is reactive with atmospheric water and it is likely that athin CeN film exposed to air will be converted to the hydroxide, therebydestroying the CeN epitaxy. Thus, it may be desirable to oxidize the CeNto CeO₂ in situ, under low oxygen partial pressure, then convert theremaining nitride layer under hydrogen/ water atmosphere ex situ, at afast conversion rate without concern over substrate oxidation.

As apparent from the foregoing and as further illustrated by severalexamples, below, various aspects of the present invention can beutilized in the context of suitable high strength metal alloysubstrates, in particular, various nickel-based substrates includingvarious non-magnetic and/or nickel alloys including but not limited toalloys of chromium and nickel. Preferred embodiments of this inventioninclude such nickel and/or nickel-chromium alloys in conjunction withthe present methodologies for preparation of oxide films. Such alloyscan also be employed in the fabrication, and as part of variousresulting composites, configured composites and/or integrated devices.In this regard, the present invention is especially useful in thecontext of superconducting wire, tape or similar such articles. Withoutlimitation, reference is made to several of the following examples. Anespecially useful nickel alloy is one comprising about 13% by weightchromium. Even so, various other non-magnetic nickel and/ornickel-chrome alloys can be used with comparable effect, as would beunderstood by those skilled in the art made aware of this invention.

EXAMPLES OF THE INVENTION

The following non-limiting examples and data illustrate various aspectsand features relating to the buffer layers, composites, articles andmethods of this invention, including the surprising and unexpectedutility of the nitride materials described herein; in particular, thefacile conversion thereof to the corresponding oxides. Comparableutilities and advantages can be realized using various otherembodiments, consistent with this invention.

Example 1

Magnetron sputtered (Zr_(0.8)Y_(0.2))N (YZN) films were grown onbiaxially textured Ni substrate, using a two temperature technique.Initially growth was done at 500° C. until the YZN thickness reached ˜30nm. Then the growth temperature was raised to 700° C. and remained thesame for rest of the deposition. Total film thickness was ˜200 nm and adeposition rate of 0.12 nm/sec. The films showed good in-plane andout-of-plane alignment. FIG. 1 shows a XRD θ-2θ scan, and FIG. 2 showsthe (111) pole figure. The existence of only four peaks demonstrates asingle epitaxial orientation. The location of the peaks in the (111)pole figure is consistent with a cube-on-cube epitaxial relationship.The YZN (111) phi scan showed a full-width-half-maximum (FWHM) obtainedby fitting a Gaussian curve to the data to be 10.5°. The FWHM is onlyslightly better than that of the underlying Ni with a FWHM of ˜8.2°. Therocking curves FWHM (the out-of-plane texture) of the YZN layer wasfound to be 3.4° in rolling direction. This is almost 2° sharper thanthe underlying Ni substrate (5.5°).

Example 2

Magnetron sputtered (Zr_(0.8)Y_(0.2))N (YZN) films were grown at asubstrate temperature of ˜550° C. on biaxially textured nickelsubstrates at a deposition rate of 0.12 nm/sec. The films had athickness of 50 nm. The films showed in-plane and out-of-planealignment. FIG. 3 shows a XRD θ-2θ scan, shows intense (200) peak. Thepresence of a (111) peak indicates that this sample has substantial outof plane texture in (200) direction but is not epitaxial. FIG. 4 showsthe (111) phi-scan from same sample. The location of the peaks in the(111) phi peaks is consistent with a cube-on-cube epitaxialrelationship. The YZN (111) phi scan showed a full-width-half-maximum(FWHM) obtained by fitting a Gaussian curve to the data to be 10.9°,indicating the grains that aligned to (200) orientation in out-of-planedirection also has some in-plane textures. The rocking curve FWHM (theout-of-plane texture) of the YZN layer was found to be 5.8° in rollingdirection. Further deposition at a sample condition to increasethickness of YZN film resulted in polycrystalline YZN layer without anyin-plane orientation.

Example 3

Y_(0.5)Z_(0.5)N films have been grown on single crystal MgO usingreactive magnetron sputtering in order to study the solid solution rangein the YN—ZrN system. Growth was carried out in Ar—N₂ mixtures. Typicalgrowth temperatures ranged from 400° C. to 800° C. and typical growthrates were ˜0.2 nm /sec. For deposition of Y_(0.5)Z_(0.5)N, 99.95% pureY and Zr targets were used. FIG. 5 shows θ-2θ x-ray diffraction (XRD)scan of a nominal Y_(0.5)Z_(0.5)N film grown on MgO. The thickness offilm was ˜500 nm. The pattern clearly shows presence of both YN and ZrNphases suggesting a phase miscibility gap existing in the YN—ZrNpseudo-binary system.

Example 4

Oxidation of the YZN films was carried out in a tube furnace inhydrogen-water vapor mixtures. The temperatures ranged from 700 to 850°C. and the time was 30 sec to 20 minute. The films showed in-plane andout-of-plane alignment comparable to the YZN source material. FIG. 5shows a XRD θ-2θ scan, and FIG. 6 shows the (111) phi-scan plot. Theexistence of only four peaks demonstrates a single epitaxialorientation. The location of the peaks in the (111) pole figure isconsistent with a cube-on-cube epitaxial relationship. The YSZ (111) phiscan showed a full-width-half-maximum (FWHM) obtained by fitting aGaussian curve to the data to be 11.0°. The FWHM of the rocking curves(the out-of-plane texture) of the YSZ layer was found to be 4.8° inrolling direction.

FIG. 8 and FIG. 9 show a scanning electron micrograph from the surfaceof the as deposited YZN and YSZ film formed by oxidation of YZN,respectively. The layer is smooth and flat surfaced. No evidence ofmicrocracking, spalling or gas bubbles was seen. Even for the case ofthick YSZ layers, no cracks were observed.

The results of this example illustrate several aspects of the invention,including the following:

-   Excellent epitaxy of YZN can be obtained on biaxially textured Ni    using reactive sputtering and two temperature technique.-   The out-of-plane texture of the YZN layer is found to be    significantly improved over that of Ni substrate.-   Excellent epitaxy of YSZ films can be obtained on biaxially textured    Ni via a simple oxidation procedure.-   The resulting YSZ films are smooth with no evidence of any    microcracking.-   The thickness of the YSZ film was larger than YZN due to a higher    molar volume for YSZ.

Example 5

Magnetron sputtered (Zr_(0.8)Y_(0.2))N (YZN) films are grown onbiaxially textured nickel substrates at a high deposition rate at lowertemperature than that is used without substrate bias. The substrate biasresults argon ion-bombardment suppressing 3 dimensional island growth,thereby facilitating YZN layers. The films have a thickness of 200 nm.X-ray diffraction characterization shows an epitaxy of YZN layer, i.e.,the in-plane and out-of-plane texture, without presence of unwantedout-of plane orientation, such as (111).

Example 6

A dual opposed cathode magnetron source configuration is used to deposit(Zr_(0.8)Y_(0.2))N (YZN) films at a low substrate temperature withrelatively lower substrate bias on biaxially textured nickel substratesat a high deposition rate. The sputtering source is set to face eachother and magnets are configured so that magnetic field around substratesitting in between two sources is maximized. This results in anincreased ion-bombardment on to the substrate and lower bias onsubstrate, allowing epitaxy of YZN without excessive compressive stresstypically associated with ion-bombardment. This also allows depositionof epitaxial nitride layer on both side of metal/alloy substrate atsingle deposition run.

Example 7

Magnetron sputtered thin cubic nitrides layers are first grown at asubstrate temperature of 600° C. on biaxially textured RABiTSsubstrates, followed by the deposition of a thick YZN layer at arelatively high deposition rate. Cubic metal nitrides first depositedinclude TiN, VN, CrN, and CeN. The nitride layers have thicknesses of˜10 nm and ˜200 nm for thin initial nitride and subsequent YZN,respectively. These cubic nitride seed layers presumably are much betteroriented compared with thin YZN directly deposited on Ni, due to theirsmaller lattice mismatch with Ni (2˜20%) compared to that between YZNand Ni (˜31%). The CeN shows best lattice match of ˜2% with a 45°rotation of the CeN lattice along (001) axis. Furthermore, higherquality of epitaxial YZN is obtained on these cubic nitrides comparedwith direct growth of YZN on Ni, since the lattice mismatch betweenthese layer and YZN is relatively smaller ˜8–11%). Subsequent oxidationproduces epitaxial oxide layer composed of YSZ on thin epitaxialTiO_(x), VO_(x), α-Cr₂O₃, CeO₂. TiN and VN pseudomorphically converts toepitaxial oxides with phases having relatively small lattice mismatchwith Ni and YSZ. Though α-Cr₂O₃ has corundum structure with hexagonalsymmetry, thin layer of CrN pseudomorphically converts to α-Cr₂O₃ withsuch orientations that has epitaxial relationship and relatively smalllattice mismatch with (001) YSZ, i.e. (101_(—)2). Such an epitaxialrelationship was previously found on epitaxial YSZ layer/α-Al₂O₃substrate. Conversion of epitaxial CrN/YZN is advantageous compared withother nitride/YZN configuration, since α-Cr₂O₃ has better oxidationresistance and mechanical toughness than TiO_(x), VO_(x) or CeO₂.

Example 8

Combinations of some cubic nitrides, such as TiN, VN, ZrN, CrN, AlN andalloys (M1,M2)N, where M1 is either Ti or V, and M2 is either Cr or Al,are deposited by magnetron sputtering at a substrate temperature of500–600° C. on biaxially textured RABiTS substrates, followed by thedeposition of a YZN layer. The thickness of YZN is ˜50 nm, while totalthickness of the underlying nitride layer ranges 200˜400 nm. Acontrolled oxidation converts top YZN to epitaxial YSZ, preservingunderlying nitrides. Especially with underlying CrN or (M1,M2)N, whereM1 is either Ti or V, and M2 is either Cr or Al, high oxidationresistance of nitride prevents oxidation of bulk nitride layer duringYBCO growth process. A thin non-epitaxial Al₂O₃ or Cr₂O₃ layer may formunder YSZ layer during YBCO growth process, but this does not effect thegrowth of YBCO, since YSZ layer is already epitaxial. Furthermore, Al₂O₃or Cr₂O₃ layers do not reduce overall mechanical toughness of the bufferlayers, since they remain thin. The thickness and composition of thesebulk nitride layers can be tailored depending on the depositioncondition of specific YBCO growth process used.

Example 9

A thin CeN and (Sr,Ti)N, (La,Al)N layer are deposited on top of YZNbuffer layers grown on Ni. (Sr,Ti)N grows on YZN epitaxially, sincestrontium mononitride has B1 rocksalt structure same as TiN. However,thin layer of these nitrides is not stable under air. Specifically,rare-earth nitride, like CeN is known to react with atmospheric moistureand convert into hydroxides upon air exposure. Thus an in-situ oxidationwith oxygen gas is used to convert CeN, (Sr,Ti)N, and (La,Al)N to CeO₂,SrTiO₃ and LaAlO₃ without taking the sample out of deposition chamber. Acontrolled conversion of top layers is straightforward for an in-situoxidation. These thin oxide top layers are advantageous, because theylattice match to YBCO better (<0.1%) than that of YSZ.

Example 10

Epitaxial rocksalt structure (Y,Zr)C layers are grown at a substratetemperature of 600° C. on biaxially textured nickel substrates at adeposition rate of 1 Angstrom/second using either (Y,Zr)C target or(Y,Zr) alloy target with carbon-providing reactive gas such as methane.Subsequent oxidation under hydrogen/water vapor mixture converts (Y,Zr)Clayers to epitaxial YSZ layers. Since the carbon contamination of YBCOis detrimental to its superconducting properties, a complete conversionof carbide to oxide is important. Thus, stronger oxidizing agents suchas oxygen, ozone, peroxide or metal-organic oxygen sources are alsoused.

Example 11

PLD can be used to deposit YBCO on the YSZ/Ni fabricated by methodsdescribed in Example 3. FIG. 10 is a θ-2θ x-ray diffraction (XRD) scanof the YBCO/YSZ/Ni multilayer sample. The primary peaks are thatcorresponding to YSZ (002), Ni (002), and YBCO (00l). This indicates theout-of-plane orientation expected for the epitaxial multilayerstructure. In order to uniquely determine the epitaxy, it is necessaryto measure phi-scans and rocking curves from the multilayer structure.The phi-scan of the Ni (220) reflection indicated a FWHM of ˜9.2° forthis sample. The phi-scan of the YSZ (220) reflection indicated a FWHMof ˜12.6°. The phi-scan of the YBCO (103) reflection indicated a FWHM of˜15°. This data is shown in FIG. 11 and 12.

Example 12

An epitaxial YZN film has been grown on Sapphire substrate andsubsequently in-situ oxidized using oxygen gas to fabricate thinYSZ/YZN/sapphire structure. The range of oxygen pressure and oxidationtemperatures used for were between 10^(−6–10) ⁻² Torr and 700˜950° C.,respectively. FIG. 13( a) is a θ-2θ x-ray diffraction (XRD) scan of atypical film, showing only YZN (002) and YSZ (002) peak from as oxidizedYZN films. The off-axis phi-scan of the TiN (220) and YSZ (220) peaksshown in FIGS. 13( b) and (c) respectively, verifies the cube-on-cubeepitaxial orientation of YSZ on YZN. The slightly larger FWHM from YSZ(˜5.9°) compared to that of YZN (220) (˜5.0°) is probably due torelatively large lattice mismatch between YSZ and YZN (˜10.4%). Therocking curve FWHM (˜1.2°) for this thin YSZ film is better than thatfrom typical YZN.

Example 13

Oxidations of the epitaxial nitride films described in earlier examples(including YZN) can be carried out in a tube furnace in hydrogen-watervapor mixtures. The oxidation conditions and processes can be chosensuch that the epitaxial nitrides are converted to epitaxial oxide andformation of a thin NiO is allowed at the interface of epitaxial oxideand Ni substrate. Such a structure shows a better adhesion compared toNi/epitaxial oxide without interfacial NiO because Ni/NiO showsinherently better adhesion due to Ni—Ni bonding in the interface, whileNiO/other epitaxial oxides also shows good adhesion between oxides.

Example 14

Magnetron sputtered (Zr_(0.8)Y_(0.2))N (YZN) films were grown on singlecrystal Si substrate, using two temperature technique. Initially growthwas done at 600° C. until the YZN thickness reached ˜40 nm. Then thegrowth temperature was raised to 900° C. and remained the same for restof the deposition. Total film thickness was ˜200 nm and a depositionrate of 0.12 nm/sec. As grown YZN film on Si was partially oxidized in atube furnace under hydrogen-water vapor mixtures. The annealingtemperature was 750° C. and the time was 30 sec. FIG. 17( a) shows a XRDθ-2 θ comparing before the oxidation. The scan shows YZN (200) peakonly, indicating a strong out-of-plane texture. FIG. 17( b) shows the(111) pole figure from as deposited YZN film on Si. The existence ofonly four peaks demonstrates a single epitaxial orientation. Thelocation of the peaks in the (111) pole figure was consistent with acube-on-cube epitaxial relationship. The YZN (111) phi scan showed afull-width-half-maximum (FWHM) obtained by fitting a Gaussian curve tothe data to be ˜9°. FIG. 17( c) shows a XRD θ-2 θ scan after theoxidation. In addition to an intense YZN (200), much smaller butdistinctive YSZ (200) peak is present, suggesting that a thin YSZ filmshas been formed, on thicker underlying YZN film. There are no otherpeaks that can be seen, indicating strong out-of-plane texture of YSZfilms. The rocking curves FWHM (the out-of-plane texture) of the YZNlayer was found to be ˜2° similar to that of underlying epitaxial YZNlayer.

Example 15

Standard Pulsed Laser Deposition (PLD) was used to deposit ˜20 nm thickceria layers on YSZ buffers, prepared by Applied Thin Films, Inc.(ATFI), in order for better lattice match with YBCO. The ATFI YSZ wasconverted from YZN using oxidation procedures described herein.Epitaxial YBCO (˜250 nm thick) was subsequently deposited by PLD. FIGS.20–23 show typical phi-scans from YBCO/ceria/ATFI YSZ/Ni-RABiTS™ withcorresponding FWHM: FIG. 20 Ni (111): 9.22°, FIG. 21 ATFI YSZ (111):10.04°, FIG. 22 CeO₂ (111) ˜9.52° and FIG. 23 YBCO (103) ˜9.97°.

Example 16

Subsequent to YBCO growth, Jc and Tc superconductivity measurements weredone on a ceria-capped ATFI YSZ buffer such as that prepared in Example15. FIG. 24 shows a representative I-V curve from Jc measurement on 200nm thick YBCO, showing Ic=6 amps at 1 μV/cm criterion. The width of filmwas 3 mm, resulting in calculated Jc of 1 MA/cm². This Jc value wasprecisely reproduced for a subsequent sample, with I-V curve almostidentical for both samples.

Example 17

Magnetron sputtered (Zr_(0.8)Y_(0.2))N (YZN) films were grown on abiaxially textured Ni substrate, using a two-temperature technique ofthis invention. Initially growth was done at 570° C. until the YZNthickness reached ˜40 nm. The growth temperature was then raised to 810°C. and maintained thereat for the remainder of the deposition. Totalfilm thickness was ˜200 nm, achieved at a deposition rate of 1.2Angstrom/sec. The films showed good in-plane and out-of-plane alignment.FIG. 25 shows a XRD θ-2θ scan, and FIG. 26 shows the (111) phi scan. Theexistence of only four peaks demonstrates a single epitaxialorientation. The location of the peaks in the (111) pole figure isconsistent with a cube-on-cube epitaxial relationship. The YZN (111) phiscan showed a full-width-half-maximum (FWHM) obtained by fitting agaussian curve to the data to be 10.6°. The FWHM of the underlying Niwas FWHM ˜7.2°. The rocking curves FWHM (the out-of-plane texture) ofthe YZN layer shown in inset of FIG. 25 was to be 4.2° and 5.8° in andabout rolling direction. This is almost 2° sharper than the underlyingNi substrate, 6.4° and 7.5° in and about rolling direction,respectively.

Example 18

Oxidation of the YZN films deposited on a Ni—Cr (13 wt. % chromium)alloy substrate was carried out in a tube furnace in hydrogen-watervapor mixtures. The temperatures ranged from 700 to 750° C., and theannealing time was 10 minute. The films showed in-plane and out-of-planealignment comparable to the YZN source material. FIG. 27 shows a XRDθ-2θ scan, and FIG. 28 shows the (111) phi scan. The existence of onlyfour peaks demonstrates a single epitaxial orientation. The location ofthe peaks in the (111) pole figure is consistent with a cube-on-cubeepitaxial relationship. The YSZ (111) phis scan showed afull-width-half-maximum (FWHM) obtained by fitting a Gaussian curve tothe data to be 11.8°. The FWHM of the rocking curves (the out-of-planetexture) of the YSZ layer was found to be 4.6° in rolling direction.This is ˜2° sharper than the underlying Ni substrate 6.7°. This is thefirst example of epitaxial YSZ fabricated on a Ni—Cr alloy substratewithout pre-deposition of Ni prior to the oxide buffer—possible becauseunlike typical oxide deposition, precursor oxidation proceeds from thesurface. The oxidation condition and annealing time were chosen so thatnitride is oxidized without substantial oxidation of the Cr component inthe substrate. Ease of nitride growth and subsequent oxidation withoutNi pre-deposition on Ni—Cr alloy substrates demonstrates just onesubstantial advantage of this invention over conventional bufferprocessing.

Example 19

Improvement in epitaxial quality of YZN on Si (001) substrate wasobserved for a thin YZN films, when a thin ZrN buffer layer was firstdeposited prior to YZN. FIG. 29 (a) shows a θ-2θ x-ray diffraction (XRD)scan of a typical YZN (30 nm)/ZrN (20 nm)/Si (001) structure, showingintense nitride (002) peak. Intensity of (111) peak is minimal,indicating a good out-of-orientation texture. Inset shows rocking curveon Nitride (002) peak, showing typical FWHM of rocking curve scan ˜3°.The off-axis Phi scans of the nitride (111) in FIG. 10( b) shows FWHM of˜4°.

Example 20

The underlying mechanism for epitaxial YSZ formation by oxidation of YZNis believed due, at least in part, to the cooperative exchange ofnitrogen and oxygen. As the YSZ layer begins to form from the uppersurface (in the process consuming YZN) it is thought oxygen diffuses inand nitrogen diffuses out through the lattice. To confirm such amechanism for nitrogen transport through the YSZ lattice, N₂ contentanalysis was done on a partially-oxidized YSZ/YZN/Si by high resolutionTEM (FIG. 30). Nitrogen distribution can be seen with GIF elementalmapping (FIG. 31). Brighter area in the maps shows higher concentrationof nitrogen. Integrated intensity profile across the interface shows theN distribution much clearer (inset in FIG. 31). The transition area isshown by brown squares in the intensity profiles. The thickness of thetransmission area in the deposited sample is less than 17 nm. The smallthickness of transmission area confirms sharp interface between YZN andYSZ. Furthermore uniform distribution of nitrogen in YSZ indicates thatnitrogen removal during the oxidation occurs at least partially throughlattice diffusion through YSZ.

While the principles of this invention have been described in connectionwith specific embodiments, it should be understood clearly that thedescriptions, along with the chosen figures, tables, and data therein,are made only by way of example and are not intended to limit the scopeof this invention in any manner. For example, a variety of nitride thinfilms can be deposited epitaxially on a variety of suitable substrates,in particular those used in the preparation of various superconductingdevices. Likewise, a variety of conversion/oxidation conditions andparameters can be employed, as would be understood from the presentinvention with a straight-forward extension thereof, as would be knownby those individuals skilled in the art and made aware of thisinvention.

Epitaxial YSZ films on silicon, sapphire and other substrates are alsoused as templates for growth of other oxide films. For example,YSZ-buffered silicon substrates are used to grow YBCO-basedsuperconductor films to fabricate Josephson junctions and SQUIDS,ferroelectric heterostructures to fabricate next-generation DRAMS, andceramic-based magnetoresistant films as read heads for ultra highdensity magnetic information storage devices. The ability to depositepitaxial YZN at high rates using reactive sputtering and subsequent toepitaxial YSZ is also suitable for the aforementioned applications.Growth of good quality YZN directly on silicon is preferable to growthof YSZ where silica formation may interfere with epitaxy growth.

Other advantages and features of this invention will become apparentfrom the claims made thereto, with the scope thereof determined by thereasonable equivalents, as would be understood by those skilled in theart.

1. A method of preparing an oxide film, said method comprising:providing a nickel substrate material having a surface; placing anitride composition layer on said substrate surface, said nitridecomposition selected from the group consisting of transition and rareearth metal compounds and combinations thereof; and oxidizing saidnitride composition.
 2. The method of claim 1 wherein said nitridecomposition is annealed under oxidizing conditions.
 3. The method ofclaim 2 wherein said conversion is at a time and temperature sufficientto provide complete oxidation of said nitride layer.
 4. The method ofclaim 2 where said conversion is under oxygen partial pressures of lessthan about 10⁻⁶ atmosphere.
 5. The method of claim 1 wherein at leastone of water, ozone, peroxide, or metal-organic oxygen sources are usedto oxidize said nitride composition.
 6. The method of claim 1 whereinsaid nitride composition is oxidized in situ after deposition on saidsubstrate.
 7. The method of claim 1 wherein said nitride composition iszirconium nitride further including a molar percentage of yttriumnitride.
 8. The method of claim 1 wherein said substrate has a pluralityof nitride layers thereon and at least one said layer is oxidized. 9.The method of claim 8 wherein at least one said nitride layer isoxidized in situ after deposition on said substrate, and another nitridelayer is oxidized ex situ.
 10. The method of claim 1 wherein saidnitride is a zirconium nitride composition.
 11. The method of claim 10wherein said nitride composition further includes a solute.
 12. Themethod of claim 11 wherein said nitride composition is oxidized ex situto provide a first oxide film.
 13. The method of claim 12, furtherincluding direct deposition of a second oxide film on said first oxidefilm.
 14. The method of claim 1 wherein said nitride composition layeris placed on said substrate over a temperature range.
 15. The method ofclaim 1 wherein said substrate material comprises a nickel alloy. 16.The method of claim 15 wherein said substrate material is anickel-chromium alloy.